1. Field of the Invention
This invention relates to manufacturing of hard disk drives (HDD) and, more particularly, to assembly, manufacturing and inspection of hard disk drive components.
2. Description of Related Art
FIGS. 1a and 1b depict a hard drive suitable for implementing embodiments of the subject invention. FIG. 1a depicts the hard drive 100 with the cover removed, while FIG. 1b depicts an enlarged image of the preamp area of the hard drive 100. The hard drive 100 uses rotating platters (disks) 110 to store data. Each platter is rotated by a spindle (not shown) and has a smooth magnetic coated surface on which digital data is stored. Information is written to the disk by applying a magnetic field from a read-write head (not shown) that is attached to an actuator arm 120. For reading, the read-write head detects the magnetic flux emanating from the magnetic bits that were written onto the platter. Since the signals from the read/write head is very faint, a preamp 130 is provided in close proximity to the head. The preamp 130 is a chip that is mounted on a substrate 140. The substrate 140 is mounted onto a carrier plate 150, that connects to the actuator arm assembly 120. The flexible circuit loop 160 is connected to the substrate 140, to transfer signals between the preamp 130 and the associated electronics (not shown). The associated electronics control the movement of the actuator and the rotation of the disk, and perform reads and writes on demand from the disk controller.
The read/write signal transmission between the pre-amp 130 and the read-write heads, is also done over a flexible circuit, generally referred to in the industry as “flexure” with a family of traces. The flexure is not shown in FIG. 1a, but part of it, 170, is shown in FIG. 1b. The flexure 170 is connected, e.g., soldered, to a Flexible Printed Circuit (FPC) 180, which in turn connects to the pre-amp 130.
The flexure technology is well known in the art as a suspension component to propagate the signal between the circuit board and the magnetic head when writing and reading to the disk. The characteristics required for flexures used in hard disk drives are low stiffness, high electrical conductivity, and high accuracy. In general, there are two types of manufacturing processes for flexures: additive and subtractive. In the additive type manufacturing an insulating layer (e.g., a polyimide) is provided over a base layer (e.g., stainless steel) and a conductor layer (e.g., copper) is deposited on top of the insulating layer.
This type of flexure is generally referred to as ‘CIS’ (Circuit Integrated Suspension). In the subtractive type of manufacturing, a tri-laminate sheet having a base layer (e.g., stainless), an insulating layer (e.g., polyimide) and a conductor layer (e.g., copper) is the starting material. Using techniques such as etching the various elements of the flexure are defined. This type of flexure is generally referred to as ‘ILS’ (Integrated Laminate Suspension) or ‘TSA’ (Trace Suspension Assembly).
In this document, the term Flexible Printed Circuit (FPC) refers to the dynamic flex circuit connected to the pre-amp; while flexure (also referred to as CIS (Circuit Integrated Suspension)) refers to the connecting circuit used to transmit the signals between the read/write heads and the pre-amp.
In the prior art it is known to solder or bond copper conductors of the FPC, to copper conductors of the flexure tail. Due to the small sizes of the conductors, it is very critical that the conductors of the FPC and the flexure be aligned properly. However, in the prior art once the flexure is laid upon the FPC, it is sometimes not possible to visually inspect the alignment of the conductors. Poor alignment may result in shorts (solder bridging) between adjacent conductors or opens. Additionally, once the two parts are bonded or soldered, there is no possibility to inspect the integrity of the bonding and/or to make any repairs.
FIG. 2a is a top view of the prior art CIS over FPC in proper alignment, while FIG. 2b is a semi-exploded view of the CIS and FPC before soldering. In FIG. 2a, all layers are shown as transparent to enable better understanding of the layout. In FIG. 2b, the CIS copper layer 315 is exploded away from its base substrate 310 for illustration purposes. FIG. 2c illustrates a top view and a corresponding cross-section view of the prior art assembly, while FIG. 2d is a cross-section at line A-A of FIG. 2a, illustrating the prior art layout. As can be seen from these Figures, the proper alignment of the CIS and FPC cannot be verified, and errors cannot be corrected.
Other background information can be found in, e.g., U.S. Pat. Nos. 5,955,176 and 6,399,899.